This invention relates to optical fiber systems, and in particular to a method and resulting component package which provide a fiber seal.
Seals are required or desirable for a variety of optical fiber components. In optical transmitters and receivers, for example, a seal is desirable to protect the components from moisture and contaminants in the environment. Further, in certain optical relays, the component housing is filled with refractive-index matching fluid which must be contained by the seal. One example of such a component is a sparing switch which provides for the switching of the optical path to a new light source when an old light source fails. (See, for example, U.S. patent application of W. C. Young, Ser. No. 432,254, filed Oct. 1, 1982, and assigned to Bell telephone Laboratories, Incorporated. (now U.S. Pat. No. 4,407,562)
Proposals have been made previously for providing optical fiber seals. For example, U.S. Pat. No. 4,119,363 issued to Camlibel et al suggests inserting a fiber through a cylindrical tube, filling the tube with solder and heating the solder so that an hermetic seal is formed upon cooling. The tube-fiber assembly is then inserted through an aperture in the component housing and soldered thereto. To some extent, this proposal relies upon the thermal expansion mismatch between the solder and fiber to form a good seal. In U.S. Pat. No. 4,413,881 issued to Kovats, it is suggested that thermal expansion mismatches could be avoided by injecting a molten alloy of bismuth and tin into the tube containing the fiber so that a seal would form upon solidification of the alloy. The tube could then be soldered to the component housing. Alternatively, the tube could be replaced by a mold which included a cylindrical chamber for forming the seal and square section passages adjacent to the chamber for placement of the fiber. After the seal is formed, the fiber is removed from the mold and the alloy is soldered directly to the component housing.
While these proposals appear adequate, it is desirable to improve hermetic fiber seals in general by minimizing the cross-sectional area of the adhesive joint. Further, it is desirable in many instances to avoid solder seals, which require removal of the protective coating surrounding the fiber and have a tendency to make the fibers brittle. This is especially important in components such as sparing switches where some movement of the fibers occurs within the component housing. Further, it is desirable to provide some means of sealing a plurality of fibers for optical packages, such as sparing switches, which require multiple optical paths at their input and/or output.
It is therefore an object of the invention to provide an improved seal for one or more fibers in an optical package.